The long term goal of this project is to describe the cellular mechanisms and principles of organization of neural networks that mediate the control of behavior. It is focussed on the neurons in the abdominal ganglion of Aplysia california that control respiratory, circulatory and renal systems in this gastropod mollusc. During the coming grant period, the neural control of respiratory pumping, an all-or-non, stereotyped behavior that is driven by a stereotyped burst in a network of 28 trigger cells, will be studied. This project will examine the function of this behavior, the mechanisms by which it is generated, and the mechanisms by which it is modulated. Five specific hypotheses concerning this behavior will be tested: (1) Different patterns of respiratory pumping serve different autonomic functions. One pattern enhances the uptake of O2 by the respiratory system of the animal, while the other enhances renal function. (2) R15 and the R20 cells, 2 types of peptidergic modulatory neurons that increase the frequency and determine the mode of respiratory pumping in vitro, are active under different physiological conditions in vivo. (3) The stereotypes phase of the population burst in the R25/L25 network, which gives the strong mode of the behavior its all-or-none feature, is an emergent property of the synaptic connections between cells in the R25/L25 network. (4) The behavior is switched between its strong and weak modes by heterosynaptic modulation of the synaptic connections between cells in the R25/L25 network. (5) The duration of the response of the R25/L25 network to activity in R15 is determined primarily by desensitization of R15's synaptic action. This desensitization can be modulated by other synaptic. These proposed studies of respiratory pumping will provide a better understanding of: (1) The neural mechanisms that underlie fixed acts. (2) The neural mechanisms that underlie complex stereotyped behaviors. (3) The modulation of central pattern generators by peptidergic neurons. (4) The physiological function of endogenous bursting cells. (5) The functional role of desensitization. (6) The neuronal integration of autonomic function. (7) Molluscan autonomic function.